This library allows for abstract declaration of available CSS and
on these declarations, html generating code can declare that it depends
ensures that the proper links appear in the HTML head. The
implementation is based on mail system implemented by html_post/2 of
Declarations come in two forms. First of all http locations are declared
using the http_path.pl library. Second, html_resource/2 specifies HTML
resources to be used in the
head and their dependencies. Resources are
is trivial to add support for other material in the head. See
For usage in HTML generation, there is the DCG rule html_requires//1
that demands named resources in the HTML head.
About resource ordering
All calls to html_requires//1 for the page are collected and duplicates
are removed. Next, the following steps are taken:
- Add all dependencies to the set
- Replace multiple members by `aggregate' scripts or css files.
- Order all resources by demanding that their dependencies
preceede the resource itself. Note that the ordering of
resources in the dependency list is ignored. This implies
that if the order matters the dependency list must be split
and only the primary dependency must be added.
debug(html(script)). to see the requested and final set of
resources. All declared resources are in html_resource/3. The edit/1
command recognises the names of HTML resources.
- To be done
- - Possibly we should add img//2 to include images from symbolic
- - It would be nice if the HTTP file server could use our location
- html_resource(+About, +Properties) is det
- Register an HTML head resource. About is either an atom that
specifies an HTTP location or a term Alias(Sub). This works
similar to absolute_file_name/2. See location_path/2 for
details. Recognised properties are:
- Other required script and css files. If this is a plain
file name, it is interpreted relative to the declared
resource. Requirements can be a list, which is equivalent
to multiple requires properties.
false), do not include About itself,
but only its dependencies. This allows for defining an
alias for one or more resources.
- Defines that the list of requirements is ordered, which
means that each requirement in the list depends on its
- States that About is an aggregate of the resources in
List. This means that if both About and one of the
elements of List appears in the dependencies, About
is kept and the smaller one is dropped. If there are a
number of dependencies on the small members, these are
replaced with dependency on the big (aggregate) one,
actually the composition of a number of smaller ones.
- May be specified for non-virtual resources to specify
the mime-type of the resource. By default, the mime
type is derived from the file name using
Registering the same About multiple times extends the properties
defined for About. In particular, this allows for adding
additional dependencies to a (virtual) resource.
- html_current_resource(?About) is nondet
- True when About is a currently known resource.
- html_requires(+ResourceOrList)// is det
- Include ResourceOrList and all dependencies derived from it and
add them to the HTML
head using html_post/2. The actual
dependencies are computed during the HTML output phase by
- html_insert_resource(+ResourceOrList)// is det[private]
- Actually include HTML head resources. Called through
html_post//2 from html_requires//1 after rewrite by
html_head_expansion/2. We are guaranteed we will only get one
call that is passed a flat list of requested requirements. We
have three jobs:
- Figure out all indirect requirements
- See whether we can use any `aggregate' resources
- Put required resources before their requiree.
- use_agregates(+Paths, -Aggregated, -AggregatedBy) is det[private]
- Try to replace sets of resources by an `aggregate', a large
small ones to reduce the number of files that must be
transferred to the client. The current rule says that aggregates
are used if at least half of the members are used.
- current_aggregate(-Aggregate, -Parts, -Size) is nondet[private]
- True if Aggregate is a defined aggregate with Size Parts. All
parts are canonical absolute HTTP locations and Parts is sorted
to allow for processing using ordered set predicates.
- requires(+Spec)// is det[private]
- requires(+Spec, +Base)// is det[private]
- True if Files is the set of files that need to be loaded for
Spec. Note that Spec normally appears in Files, but this is not
necessary (i.e. virtual resources or the usage of aggregate
- order_html_resources(+Requirements, +AggregatedBy, -Ordered) is det[private]
- Establish a proper order for the collected (sorted and unique)
list of Requirements.
- requirements_graph(+Requirements, +AggregatedBy, -Graph) is det[private]
- Produce an S-graph (see library(ugraphs)) that represents the
dependencies in the list of Requirements. Edges run from
required to requirer.
- Subscribes a list of dependencies from resources that declare
their requirements with
- connect_graph(+Graph, -Start, -Connected) is det[private]
- Turn Graph into a connected graph by putting a shared starting
point before all vertices.
- before(+Term, -Before) is det[private]
- Unify Before to a term that comes before Term in the standard
order of terms.
- - instantiation_error if Term is unbound.
- res_properties(+Spec, -Properties) is det[private]
- True if Properties is the set of defined properties on Spec.
- same_resource(+R1, +R2) is semidet[private]
- True if R1 an R2 represent the same resource. R1 and R2 are
resource specifications are defined by http_absolute_location/3.
- html_include(+PathOrList)// is det[private]
- Include to HTML resources that must be in the HTML <head>
element. Currently onlu supports
Extend this to support more header material. Do not use this
predicate directly. html_requires//1 is the public interface to
include HTML resources.
|HTTP||- location or list of these.|
- mime_include(+Mime, +Path)// is semidet[multifile]
- Hook called to include a link to an HTML resource of type Mime
into the HTML head. The Mime type is computed from Path using
file_mime_type/2. If the hook fails, two built-in rules for
include a =.pl= files as a Prolog script, use:
html_head:mime_include(text/'x-prolog', Path) --> !,